Such rings for swaging are presently obtained by various methods.
By way of example, mention is made of the technique consisting in pressing a plane metal ring and then subsequently in cutting out the plane portion that subsists after the stamping operation. In addition to being relatively lengthy, such a method leads to a considerable loss of metal during the cutting-out operation and thus leads to the ring for swaging being excessively expensive.
It is also mentioned that rings for swaging can be obtained by slicing off suitable widths from a tube made of a sheet of metal that has been rolled into a tube and welded together along a generator line of said tube. That method is also not very satisfactory. Not only does it take a relatively long time because of the slicing, but in addition it requires prior manufacture of the tube, thereby also leading to rings for swaging that are prohibitively expensive.
Subsequent to the development of the two above-mentioned methods, the idea came about that rings for swaging could be made from a metal strip of width corresponding to the width desired for the ring. A length of strip is cut off and rolled up, and its two ends are bonded together without giving rise to significant extra thickness in the bonding zone, since that could disturb the subsequent swaging operation.
To this end, proposals have been made to butt-weld the two ends of the length of strip together after it has been rolled up. However, that operation generally cannot be performed automatically on the machines used for cutting off the lengths of strip and for rolling them up. That gives rise to a discontinuity in the manufacturing process, and also to certain fragility in the weld zone. More seriously, the need for a welding operation makes it impossible to use a strip of metal that has been treated appropriately for the subsequent swaging operation. The treatment in question must nevertheless be performed after the ring has been fabricated, and as a result the cost of the ring is likewise prohibitive.
Still in the context of fabrication from a metal strip, a final idea has been to cut out complementary shapes in the ends of a length of strip, e.g. T-shapes, which shapes are suitable for being engaged one within the other, said shapes being prevented from relative movement in the radial direction by welding, as before, in general by welding together the ends of the horizontal bar of the T-shape. However, in addition to the drawbacks mentioned above that result from the need to perform a welding operation, it is observed during the swaging operation that unacceptable deformations often occur on rings made by the above method.
The Applicant has therefore had the idea of implementing rings for swaging without any welding operation, thereby avoiding the drawbacks of known rings, in particular rings obtained by the first above-mentioned method. To this end, the Applicant proposes implementing methods that require only operations of pressing and/or stamping, cutting out, and/or folding that are suitable for being automated. Furthermore, the lack of any welding makes it possible to use a strip of metal that has been appropriately treated for the subsequent swaging operation, thereby contributing to a considerable reduction in the time required for fabricating a ring, and consequently reducing its cost price.